Intercommunication system



I 25, 5- R. H. HERRICK 2,385,515

' i I V V 'INTERCOMMUNICATION SYSTEM I Filed March 25 1944 2 Sheets-Sheet 1 ANS STATION 2 FIG. I

TO OTHER STATIONS STATION l 9 T 'INVENTOR.

ROSWELL H. HERRIGK ATTORNEY Sept. 25, 1945; R. H. HERRICK INTERCOMMUNICATION SYSTEM Filed March 25, 1944 2 Sheets-Sheet 2 INVENTOR. 5: ROSWELL H. HERRICK ATTORNEY .PDO

rob-3m Patented Sept. 25, 1945 INTERCOMMUNICATION SYSTEM Roswell H. Herrick, Oak Park, Ill., assignor to Automatic Electric Laboratories, Inc., Chicago, III., a corporation of Delaware Application March 25, 1944, Serial No. 528.030

15 Claims. (01. 179-38) The present invention relates to intercommunication systems having a plurality of stations remotely located and particularly to switching circuits'for such systems. The invention has been illustrated in connection with a system in which each station is provided with a microphone, a loudspeaker, amplifiers, power supply, control keys, and switching relays. Each station has a station selecting key corresponding to each other station. There is also a selecting relay corresponding to each other station for effecting the desired connections between stations. Auxiliary relays which are controlled over the same conductors used for communication are used for signalling and for controlling the amplifiers.

The principal object of the invention is to provide an efii'cient switching arrangement having a number of novel features such as the completion of a communication circuit without the necessity of the called party knowing the identity of the calling station, assuring privacy of the circuit thus established, automatic signalling, and the provision of a visual busy signal.

A feature of the invention is the elimination of the delay usually required for the amplifiers at the called station to warm up by energizing them at the time the call is initiated so that conversation may proceed immediately upon answering, but maintaining the amplifiers inactive until the completion of a connection to eliminate back ground noises created by stray coupling and to prevent the calling party from overhearing conversation in the vicinity of the called station prior to answering.

Other objects and features of the invention will appear upon a further perusal of the specification and the accompanying drawings in which:

Fig. l is a schematic wiring diagram of two complete stations with the necessary interconnections.

Fig. 2 is a modification of Fig. 1 that affords complete privacy of the conversation and eliminates the common lead of Fig. 1.

Referring to the drawings, the amplifiers indicated may be any conventional design having the requisite gain and output capabilities for the purpose intended and provided with transformers to match the impedances of the input and output circuits. The amplifier tubes are preferably of the quick heating type. Voice operated switching means to prevent the output of the loudspeaker from affecting the output of the amplifier associated with the microphone are indicated in block form.

, The station selector keys may be any conventional design. These keys must be the locking type for Fig. 1. The non-locking type is preferred for Fig. 2. The other keys for both figures are preferably non-locking.

The power supply indicated in block form can be any conventional design that will furnish the filament and plate voltages for the amplifiers and voice operated switching system and will also supply an isolated D. C. voltage for operating a relay'at the called station over the talking leads. The power supply must also furnish a low voltage for operation of the audible and visual signals. A separate transformer is shown in the drawings for operating the switching relays. This transformer must be continuously excited.

The method of operation will now be described briefly. Referring to Fig. 1, each station is equipped with a station selecting key corresponding to each other station. A selecting relay is also provided for each selecting key One of the input-terminals of the in amplifier, in series with a control relay; and one of the output terminals of the out amplifier at each station are multipled to contacts on the corresponding selecting relays at every other station and are also multipled to contacts on each of the selecting relays associated with that station. The other input terminal of the in amplifier and the other output terminal of the out amplifier, in series with a source of direct current, are connected to a lead which is common to all of the stations. The-operation of a selecting key operates one of the selecting relays to complete a circuit between the in amplifier at the callingstation and the out" amplifier at'the called station, and to complete a second circuit between the ou amplifier at the calling station and the 111" amplifier atthe called station. The relay in series with the input of the in amplifier at the called station is operated by the direct current source in series with the output of the out amplifier at the calling station. This relay operates and energizes the amplifiers at the called station and starts the audible signal. The amplifiers at the calling station are energized by the operation of a relay that is controlled by the selecting relays or by an answer key. Operation of the answer key at the called station causes the operation of the corresponding relay at the called station which enables the use of the amplifiers and stops the audible signal. The communicating circuit is now complete and will remain in this condition until the selecting key is restored at the calling station.

Referring now to Fig. 2, each station is equipped with a station selecting key and a selecting relay corresponding to each other station as in Fig. 1. Both input terminals of the in amplifier, in series with a control relay, are multipled to contacts on the corresponding selecting relays at every other station. Both output terminals of the out amplifier, in series with a source of direct current and a lamp, are multipled to contacts on each. of the selecting relays associated with that station. The operation of a selecting key operates one of the selecting relays which completes a circuit between the out amplifier at the calling station and the in" amplifier at the called station to establish a communieating circuit and to operate the control relay at the called station. The audible "signal at the called station. is operated and the amplifiers energized. When the call is answered by operating the answer key all of the selectingrelays at the called station are momentarily associated with their corresponding stations and the relay that corresponds to the calling station is caused to operate thereby connecting the out amplifier at the called station to the infamplifier atthe calling station. cuit is thus established. The connections will remain in this condition until-released by the operation of the releasekeys at the connected stations.

The method of operation will now-be described in detail. Referring to Fig. 1, when a party at station 1 desires to communicate with another party at station 2, he operates the station selector key IIlI assigned to station 2, closing the circuit to relay I02. Relay I02 operates and closes thecircuit to relay I03. Relay I03 operates,-prepares its lockingcircuit, removes a shortcircuit from th output of the on amplifier, opens the circuit to the audible signal I04, and closes the A. C. supplyto the powersupply-unit. Energizing thepower' supply causesthe pilot lamp I05 to light-prepares theamplifiers for use, and produces a D. C. voltage between leads I06 and I'I. The previous-operation of-relay I02 closed a circuit from the output transformer of the out amplifier of station 1, through contacts I08 .to relay I09 at station 2 through line IIO of the connecting cable, through relay I09 and the input transformer of the in-amplifier at station -2 to the common lead. The other end of the output transformer at station 1 is connected to 'the common lead through the isolated D. C. source in the power :supply. A direct current therefore flows through line Hflfrelay I09, and returns over'thecommon leadcausing relay I09 to operate. Relay I09operates, removes'a shortcircuit from theoutput ofthe in amplifier at station 2,'prepare's'a locking circuit'to'relay III, andcloses the A. C. supply to the power supply unit atstation2. Energizing the power supply unit causesthe pilot lamp IIZ to light and starts the audible signal H3 at station 2. The D. C. voltage :produced between leads H4 :and -I I at station 2 will cause a direct currentv to fiow through the output transformer of the out amplifier at station 2, over line I-I-S Of-the connecting \cable, through contacts II! of relay I02, through relay H8 and the input transformer of the in amplifier at station 1, and returning to the power supply unit at station 2 via the A second communicating cir.

common lead causing relay II8 to operate. Relay H8 operating, closes a locking circuit to relay I03 and removes a short-circuit from the output of the in amplifier at station 1.

The called party at station 2 will respond to the signal by momentarily operating the answer key .-I I9 causingrelay HI to operate and look through contacts I20 to contacts I2I of relay I09. Relay I' If I operating, opens thecircuit to the audiole signal I I3 and removes a short-circuit from the output of the out amplifier at station '2. The "complete two-way communication circuit is now established. Signals generated by-the microphoneat'sta'tion l are. amplified by the out amplifierat-station landconveyed by lead I I0 and the comm'onllead of theconnectingcable to the input ofthe in" amplifier at station .2 where they are further amplified before being reproduced by the loudspeaker at station 2. In a similar manner signals generated by the microphone at station 2 are conveyed by lead H6 and the common lead of the connecting cable to station 1 where they are further amplified by the in amplifier and reproduced by the loudspeaker. The condensers across relays I09 and H8,

and across the D. C. voltage supply for these relays .provide a low impedance path for audio frequencies.

Although the amplifiers at the called station are prepared for operation at the instant that a call is initiated the calling party cannot overhear any conversation taking place in the vicinityof the microphone at the called station before the call is answered due to the short-circuit across the outputof the out amplifier, but the loudspeaker at the called station will respond to signals produced by the microphone at the calling station.

'When'the conversation is completed the selector key at the calling station is restored, opening the circuit to relay I02. Relay I02 restoring opens the circuits to relays I09 and H0 at contacts I08 and Ill, respectively. Relays I09 and I I8 restore and open the locking circuits to relays I03 andIII. Relays I03and III restore and disconnect the A. C. supply from their associated power supply units. The pilot lamp H2 at the called station remains lit until the calling party releases the connection-to inform the called party that his microphone is still active.

Referring now to Fig. 2, when a party at station 1 desires to communicate with a party at station 2, he momentarily operates the station selector key 20I corresponding to station 2 thus closing the circuit to relay 202. Relay 202 operates, closes its locking circuit through contacts of the release key 203, and closes a circuit to relay 204. Relay 204 operates,.prepares its locking circuit, opens'the'operating circuit to relay 202 at contacts 205, opens the circuit to the audible signal 206,-removes a short-circuit from the'output of'the out amplifienandcloses the A.'C. supply to thepower supply .unit. Energizing the power supply unit prepares the amplifiers for use and causes a D. C. voltage to be produced between leads 20? and 208. This voltage causes a current to flow over a circuit previously closed by the operation of relay 202 to operate relay 209 at the called station. This circuit can be traced from lead 20'I through the output transformer of the out amplifienatstation 1, contacts 2I0, line 2I I, relay 209, the input transformer of the in amplifier at station 2, line 2 I2, contacts 2I3, and the pilot'lamp 2M to-lead=208.

The pilot lamp 2M will light and relay 209 will operate. In the event that station 2 is in use a similar circuit to relay209 would have been previously established from another station. Relay 209 would then only draw one half of its normal current from each station causing the pilot lamps at these stations to dim, thus indicating to the calling party that the called station is in use. Nowassuming station 2 is idle, relay209 operates, removes 'a short-circuit from the output of the in amplifier at station 2, prepares a locking circuit for relay 2I5, and closes the A. C. supply to the power supply unit atsta'tion-Z. Energizing the power supply unitprepares theamplifier for use, starts-the audible signal 2H5, and causes a D. C. voltage to be produced between lines 2II and 2I8. When the called party at station 2 responds to the call he momentarily operates the :answer key '2 I9, thus 'closing the circuit-to relay 220. Relay 220 operates, prepares a circuit to each line relay from its associated line, and closes a circuit to the line relay corresponding to the calling line, in this case relay 22!. This circuit can be traced from the secondary of transformer 222 through contacts of the release key 223, contacts 224, line 2 l2, contacts 2l3, contacts 225, line 226, contacts 221, and through relay 22| to the other side of the secondary of the transformer 222. The circuits to all of the other line relays at station 2 will be open at the contacts of the correspondin line relays at the other stations. Relay 22! operates over the circuit just traced, closes its locking circuit through contacts on the release key 223, closes a circuit to relay 225, and connects the output of the out amplifier at station 2 through lines 225 and 228 to the input of the in amplifier at station 1. The D. C.voltage between leads 2!! and 2l8 causes a direct current to flow through this circuit and through relay 229. Relay 2|5 operates, closes its locking circuit through contacts 233 to contacts 23E on relay 209, opens the circuit to the audible signal 2H3, removes a short-circuit from the output of the out amplifier at station 2, and opens the circuit to relay 222. Relay 220 restores and disconnects the line relays from their associated lines. This entire operation actually takes place in a few milli-seconds while the answer key 2!!! is operated by the called party. Relay 229 operates over the circuit previously described, closes the locking circuit to relay 204 at contacts 232, removes the short-circuit from the output of the in amplifier at station 1, and opens the tie between the input of the in amplifier and the output of the out amplifier at contacts 225. The complete communication circuit is now established and conversation can proceed. The signals produced by the microphone at station 1 are amplified by its associated amplifier and conveyed to the input of the in amplifier at station 2 over lines 2!! and 2:2. In like manner, signals produced by the microphone at station 2 are amplified by its associated amplifier and conveyed to the input of the in amplifier at station 1 over lines 225 and 228. The condensers across relays 209 and 22S, and across the D. C. voltage supply for these relays provide a low impedance path for audio frequencies. Although the amplifiers at the called station are prepared for operation at the instant that a call is initiated the calling party cannot overhear any conversation taking place in the vicinity of the microphone at the called station before the call is answered because this portion of the communicating circuit is open at contacts 233 and 234 of the line relay 22!. The short-circuits across the outputs of the amplifiers is an additional precaution to prevent any signal from reaching 'the loudspeakers due to stray coupling before a connection is establish-ed- If either station 1 or station 2 is called by a third station while they are connected, the third station. will have the output of its out amplifier connected to the input of the in amplifier at the station called, but the line relay at the called station corresponding to the third station will not be operated and will therefore prevent the party at the third station from overbearing the conversation already in progress, but will permit the third party to speak to the party he called. If he message is urgent the first connection established can be released and the answer key operated at the station called by the third party to establish a new connection.

When the conversation between stations 1 and 2 is terminated the connection is released by the momentary operation of the release key at each station. Assuming that the party at station 1 disconnects first, Operation of the release key 203 opens the locking circuit to relay 202. Relay 202 restores, opens the operating circuit to relay 204, and disconnects the output of the out amplifier and the D. C. voltage supply from lines 2 and H2 thus opening the circuit to relay 209. Relay 204 remains locked to relay 229 to prevent reoperation of the audible signal 206. Relay 209 restores, opens a multiple circuit to relay 2| 5 and short-circuits the output of the "in amplifier at station 2. When the release key 223 at station 2 is operated momentarily, the locking circuit to relay 22! is opened. Relay 22! restores, opens the circuit to relay 2 l5 and disconnects the output of the out amplifier and the D. C. voltage supply from lines 226 and 228 thus opening the circuit to relay 229. Relay 2l5 restores and disconnects the power supply unit at station 2 from the A. C. supply. Relay 229 restores and opens the locking circuit to relay 204. Relay 204 restores and disconnects the power supply unit at station I. from the A. C. supply.

It is to be understood that the form of the invention herewith shown and described is to be taken as a preferred example of the same, and that various modifications may be resorted to without departing from the spirit of the invention or the scope of the subjoined claims.

Having thus described the invention, what is claimed as new and desired to secure by Letters Patent is:

1. In an intercommunicating system including a plurality of stations, each comprising voice receiving and transmitting means, a direct current source associated with each said transmitting means, a relay associated with each said receiving means, conductors for each station, switch ing means at each station, said switching means being operated at one station to selectively connect the transmitting means of said one station and the receiving means of an other station via said conductors to simultaneously complete a talking circuit therebetween and energize the relay at said other station by the source of direct current at said one station over the same said conductors. V

2. In an intercommunicating system as claimed in claim 1, a lamp in series with each said direct current source, and circuit arrangements causing the lamp at said one station to indicate if said other station is in use when the transmitting means of said one station is connected to the receiving means of said other station.

3. In an intercommunicating system including a plurality of stations, each comprising voice receiving and transmitting means, station selecting keys, an answer key, and an audible signal, means controlled by the operation of one of said selecting keys for connecting one of the stations to another to complete a communication circuit between the transmitting means of said one station and the receiving means of the other station, relay switching means at said other station also controlled by the operation of the associated selecting key at said one station to operate said audible signal at said other station and operated in response to the operation of said answer key at said other station to stop the operation of said audible signal.

4. In an intercommunicating system including a plurality of stations, each comprising voice receiving and transmitting means, station selecting keys, and an answer key, meansresponsive to the operation of a selecting key at one of said stations for connecting it with another of said statio'ns and'enabling the transmitting means at said one station and the receiving means at said other station, and means responsive to the operation of "said answer key at'saidother station enabling the transmitting means at said other station and the receiving'means atsaid one-station.

5. In-an intercommunicating system including azplurality'of stations, each comprising voice'receivirig and transmitting means, amplifying means therefor, and station selecting keys, relay switching means at each station operative in response tothe'operation of any one of said selecting' keys 'at-one station to connect-that station with another station and to energize the amplitying means at said one station and at the sta tion associated with'said selecting key.

'6. In an intercommunicating system including a-plurality of stations, each comprising voice receiving and transmitting means, amplifiers for said receiving and transmitting means, station selecting keys, and an answer key, relay switching means at each station operative in response to the operation of any one of said selecting keys at one station to connect that station with another station and to energize the amplifiers at said one station and at the station associated with said selecting key and to enable operation of the transmitting means at said one station and the receiving means at said other station, said relay switching means operated in response to the-operation of said answer key at said other station to enable operation of the transmitting means at said other station and the receiving means at said'one station.

'7. In an intercommunicating system including a plurality of stationseach having an input and an output circuit, and a selecting relay corresponding to each other station, means at each station for at times associating the input and output circuits thereof, conductors associated with the input circuits of each station and multipled to the corresponding selecting relays at every other station, means for operating a selecting relay at one station to connect the output circuit of said one station to the input conductor of another station to thereby associate the input conductors of said two stations, means for causing said selecting relays at said other station to test all of said conductors and to connect the output circuit of said other station to the input conductor-of said one station which is identified by said association between the input conductors of said two stations.

8. In an intercommunicating system as claimed in claim '7, a release key at each station, and cir cuit arrangements maintaining said connections under control of the release keys of the connected stations,

9. In an intercommunicating system as claimed in claim '7, circuit arrangements preventing the re-operation of said selecting relays at said other station while said other station is connected to said one station to assure privacy of said connection.

10. In a telephone system, a plurality of stations, a relay at each station corresponding to each other station, means for extending a 'connection from a calling one of said stations to a called one of said stations, means for causing'all of-the relays at the called station to be associated with their corresponding stations and for operating only that relay at the called station which corresponds to the calling station.

11. In an intercommunicating system, a plurality of stations, a relay at each station corresponding to each other station, means for operating any one of the relays at a calling one of said stations to connect that station with a called one of said stations corresponding to said one relay and for signalling said called'station, and means at the called station operated when the party thereat responds to said signal for causing all of the relays thereat to be associated with their corresponding stations and operating only that relay which corresponds to the calling station.

12. In an intercommunicating system, a plurality of stations, each having an input and an output circuit, and a selecting relay corresponding to each other station, conductors associated with the input circuits of each station and mul tipled to the corresponding selecting relays at each other station, means including said relays for connecting the output circuit of any one of said stations to the input circuit of any other station, means at said other station for connecting a voltage source between the input circuit of said other station and said conductors through the selecting relays at said other station, circuit arrangements at said one station to complete a circuit only to the selecting relay at said other station that corresponds to the said one station.

13. In an intercommunicating system as claimed in claim 3, a direct current source associated with the transmitting means at said one station, said relay switching means being associated with the receiving means at said other station 50 as to be controlled by said source over the same conductors over which said communication circuit is completed.

14. In an intercommunicating system including a plurality of stations, each comprising voice receiving and transmitting means, station selecting keys, an answer key, and an audible signal, means controlled by the operation of one'of K said selecting keys for connecting one of the stations to another to complete a pair of oppositely directed communication channels between the transmitting and receiving means of said two stations, one of said channels being disabled, means at said other station also controlled by the operation of the associated selecting key at said one station to operate said audible signal at said other station, and means operated in response to the operation of said answer key at said other station to stop the operation of said audible signal and to enable said one channel.

15. In an intercommunicating system including a plurality of stations, each comprising voice receiving and transmitting means, station selecting keys, an answer key, and an audible signal, means controlled by the operation of one of said selecting keys for connecting one of the stations to another and enabling the transmitting means at said one station and the receiving means at said other station, means at said other station also controlled by the operation of the associated selecting key at said one station to operate said audible signal at said other station, and means operated in response to the operation of said answer key at said other station to stop the operation of said audible signal and enable the transmitting means at said other station and the receiving means at said one station.

ROSWELL H. HERRICK. 

